People will have to cut meat from their diets if the world is to stay within safer limits of planet-warming greenhouse gases, nitrate pollution and habitat destruction, according to a report published Monday in the Proceedings of the National Academy of Sciences.

Experts agree that eating plant products can be better for the environment, because eating meat involves consuming animals which are themselves raised on plants, a less efficient process.

But there is some controversy about just how far people should shun meat for vegetables and grains to curb damage to the environment, partly because of wide disagreement about exactly what those impacts are.

The paper used coarse estimates to argue that, on current trends, livestock farming on its own - disregarding all other human activity - would push the world near danger levels for climate change and habitat destruction by mid-century.

“We suggest that reining in growth of this sector should be prioritised,” said the authors from Canada’s Dalhousie University, in their article titled “Forecasting potential global environmental costs of livestock production 2000-2050”.

The paper described “a profound disconnect between the anticipated scale of potential environmental impacts associated with projected livestock production levels and even the most optimistic mitigation strategies”.

Solutions to the problem included using best practice such as substituting manure for nitrogen fertilisers, and increasing agricultural productivity, said the paper published

But efficiency gains would not be enough. Per capita meat consumption would have to be cut.

“Across the board reductions in per capita consumption of livestock products should ... be a policy priority,” it said.

The paper calculated required cuts in globally averaged per capita meat consumption of 19-42 percent by 2050, given expected increases in population and income, just to stand still regarding environmental damage.

Livestock farming drives emissions of the greenhouse gas methane, from the stomachs of ruminants and especially cattle, and of carbon dioxide by increasing deforestation.

Intensive farms also use fertilisers which release the powerful greenhouse gas nitrous oxide when applied to the soil.

Both fertilisers and manure release nitrogen into natural systems such as rivers, upsetting the natural balance.

Farming also competes with natural habitats. The human food system already consumes 12 percent of the output of all the world’s plants, the paper said.

SOURCE:  Proceedings of the National Academy of Sciences, online October 4, 2010.